This invention relates to a coolant feeding device of a machine tool.
Prior art references (such as the Japanese Patent Publication No. 66437 of 1997) have disclosed machine tools that feed coolant from a feed pump to a mist generating device at the tip of a spindle through a feed line, and that is provided with a valve means at a coolant inflow portion of the mist generating device. Here, the valve means is to close a coolant path when coolant pressure within the feed line lowers below a fixed level.
In the above conventional machine tools, compressed air is mingled with the coolant inside the feed line, fed from the mist generating device. When the feed pump stops feeding the coolant, compressed air pressure lowers, and then the air expands, thereby causing a little coolant leakage out of the valve means (this phenomenon is called liquid dropping).
The liquid dropping is a waste of coolant. Besides, it widens a timi-lag between the onset of the feed pump and mist production by the mist generating device. Moreover, when generating mist again, the coolant which remains in the mist generating device may spout at a stretch, thereby polluting a work piece and a working environment.
An object of this invention is to provide a coolant feeding device of the machine tool that can solve the above problems.
To achieve the above object, the present invention is characterized by a machine tool that feeds coolant from a feed pump to a mist generating device on the tip of a spindle by way of a feed line. In this machine tool, a cylinder chamber for compressed air and a cylinder chamber for coolant are provided oppositely. Besides, pistons (30) (31) are provided to the cylinder chambers (28) (29), respectively, and integrated into one body. Moreover, a coolant sucking and delivering means is provided with a compression spring to press the pistons in a specific direction for each cylinder chamber. The means sucks a fixed amount of coolant in the feed line, when the feed pump stops feeding the coolant. Furthermore, the means feeds a fixed amount of coolant into the feed line, when the feed pump begins feeding the coolant.
When the above coolant sucking and delivering means sucks the coolant, the coolant pressure within the feed line lowers at a stretch. Accordingly, usual liquid dropping is prevented.
Beside, when the coolant sucking and delivering means spouts the coolant, the coolant pressure within the feed line rises at a stretch. Accordingly, the coolant is immediately fed into the mist generating device in connection with the onset of coolant feed from the feed pump, thereby bring about a good response of mist generation.
This invention can be materialized as follows.
At a coolant inflow part of the mist generating device is provided a valve means that is closed when the coolant pressure within the feed line is below a fixed level. The valve means is closed immediately, when the feed pump stops feeding the coolant. Therefore, usual liquid dropping is prevented more certainly. On the other hand, when the feed pump begins feeding the coolant, the valve means is open immediately. This enables rapid mist generation.
Besides, the coolant sucking and delivering means sucks the coolant inside the feed line into the cylinder chamber at need, and discharges the sucked coolant into the feed line at need. According to this means, sucking and discharging coolant is easy.
Moreover, the piston is driven by a compressed air fed into the mist generating device for producing mist. Since the compressed air for producing the mist is used for driving the piston, driving mechanism for the piston is simplified.